Bypass circuit and wipe technique for contactor used to operate solid state relays that control heating elements

ABSTRACT

A control circuit for a cooking oven. The control circuit includes a contactor. The contactor has at least one contact and at least one coil. A relay (such as a solid-state relay) is in series connection with the contactor. A heating element is controlled by the relay and is in series connection with the relay and the contactor. The controller also includes a controller. The controller is configured to bypass the relay and to control power to the at least one coil.

BACKGROUND

The present invention relates to heating circuits and, moreparticularly, to heating circuits in conveyor ovens.

Electric heating elements are used in infrared cooking ovens, includinginfrared conveyor ovens used to cook pizzas and other foods. Electricheating elements can be controlled by solid-state, zero-cross relays. Inparticular, the supply of electrical power to the heating elements iscontrolled by the relays. Electrical noise is generated when relaycontacts open and close and zero-cross relays generate less noise thanother types of relays. As with most components, solid-state relays aresubject to failure and if a relay fails in the on position, a constantsupply of power is provided to the heating element. This could lead toover-heating and other hazards. A coil-activated or triggered contactorcan be used in the circuit prior to (or in series with) the solid-staterelays to provide a safety (or circuit break) in case a solid-staterelay fails in the on position. A high-temperature-limit-control switchoperates the contactor coil and, if the high limit is tripped, the coilto the contactor is de-energized and the contactor opens. When thecontactor opens, the supply of power to the heating element isinterrupted.

SUMMARY

Recently, the materials used in contactors have changed. In particular,the metal used for contacts in contactors has been changed to silver.Silver replaced other metal for environmental reasons. It is believedthat silver contactors oxidize during normal use of the conveyor oven.Once a contactor is contaminated, such as by oxidation, thecontamination creates a resistance high enough to prevent power fromflowing through the contactor; even if the contacts of the contactorsare in a closed position. Thus, the electric heating elements do notreceive power, and cannot cook food.

In one embodiment, the invention provides a control circuit for acooking oven. The control circuit includes a contactor that has at leastone contact and at least one coil; a solid-state relay in seriesconnection with the contactor; and a heating element controlled by thesolid-state relay. The heating element is in series connection with thesolid-state relay and the contactor. The controller is configured tobypass the solid-state relay, and control power to the at least onecoil.

In another embodiment, the invention provides a method for controlling acooking oven, the cooking oven including a housing and a heatingelement. The method comprising placing in a series-type configuration, arelay, a contactor including at least one contact and at least one coil,and the heating element. The method further comprising controlling abypass of the relay; and controlling power to the at least one coil;wherein the heating element is controlled by the relay.

In another embodiment, the invention provides a method of controlling acooking oven having at least one heating element and at least onecontactor, the at least one contactor having an associated coil. Themethod comprising receiving, at a controller, a signal from a user powerswitch; generating, with the controller, a signal to activate one ormore first relays; shorting one or more second relays subsequent toactivating the one or more first relays; connecting the at least onecontactor directly in series with the at least one heating element;energizing the coil of the at least one contactor; and de-activating theone or more first relays.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an infrared conveyor oven.

FIG. 2 is a circuit diagram of an infrared conveyor oven having aplurality of heating elements, solid-state control relays, and twocontactors.

FIG. 3 is a block diagram of a controller of an infrared oven.

FIG. 4 is a flow diagram of a process for controlling the temperature ofan infrared oven.

FIG. 5 is a circuit diagram of an infrared conveyor oven having aplurality of heating elements, two contactors, and a high-amp bypasscircuit.

FIG. 6 is a block diagram of the high-amp bypass circuit.

FIG. 7 is a flow diagram of a process for controlling power to aplurality of heating elements.

FIG. 8 is a flow diagram of a process for controlling power to aplurality of heating elements.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

FIG. 1 is a perspective view of an infrared conveyor oven 1. Theconveyor oven 1 includes a housing 5 and conveyor 7. The housing 5encloses the electrical components 10 (shown in FIGS. 2 and 5) of theconveyor oven 1. The conveyor 7 is made of a metal woven wire mesh andis used to transport food through the conveyor oven 1. The conveyor 7 iscoupled to a motor 11 (shown in FIGS. 2 and 5), which moves the conveyor7 through the conveyor oven 1.

FIG. 2 is a circuit diagram illustrating the electrical components 10 ofthe conveyor oven 1. The conveyor oven 1 generally includes heatingelements 15, solid-state control relays 20, temperature sensors 25,contactors 30A and 30B, a temperature switch 35, and a controller 40. Inthe embodiment shown, a power supply 45 provides 230V AC voltage to theelectrical components 10. It is possible that the conveyor oven 1 andelectrical components 10 could be designed to operate using a differentpower supply voltage (and current). The heating elements 15, solid-statecontrol relays 20, and contactors 30A and 30B are connected in aseries-type configuration. In the embodiment shown, there are twocontrollers 40, one controlling the upper set of heating elements, andone controlling the lower set of heating elements. In the embodimentillustrated, the controllers are substantially identical.

The phrase “series-type configuration” as used herein refers to acircuit arrangement where the described elements are arranged, ingeneral, in a sequential fashion such that the output of one element iscoupled to the input of another, but the same current may not passthrough each element. For example, in a “series-type configuration,” itis possible for additional circuit elements to be connected in parallelwith one or more of the elements in the “series-type configuration.”Furthermore, additional circuit elements can be connected at nodes inthe series-type configuration such that branches in the circuit arepresent. Therefore, elements in a series-type configuration do notnecessarily form a true “series circuit.”

The heating elements 15 are electrical loads that produce infrared lightto produce heat. The heating elements 15 receive power from the powersupply 45 and, in the embodiment illustrated, produce long-wave,infrared light to cook food.

The solid-state control relays 20 control the supplied power to theheating elements 15 (and, thus, can be considered power control relays).The solid-state control relays 20 are electronic switching devices thatswitch the power to the heating elements 15 on or off. In someembodiments, the solid-state control relays 20 do not contain movingparts, thus minimizing any electrical noise when switching the suppliedpower on or off. In other embodiments, the solid-state relays 20 containmoving parts.

The contactors 30A and 30B further control the supplied power to theheating elements 15. The contactors 30A and 30B act as a safety, in casea solid-state control relay 20 fails. The contactors 30A and 30B areelectronic switching devices that control the power to the heatingelements 15, through the solid-state control relays 20. The contactors30A and 30B include contacts and coils. When the coil is energized orpowered, the contacts close together, allowing current to flow to theheating elements. If the coil is de-energized, the contacts are open,and current is not supplied to the heating elements 15.

The temperature switch 35 senses the temperature of the oven andcontrols the power to the coils. The temperature switch 35 providespower to the coils if the sensed temperature of the oven is under asafety shutoff temperature (approximately 975° Fahrenheit). If thesafety shutoff temperature is met, the temperature switch 35 disconnectsthe power to the coils of the contactors 30A and 30B opening thecontacts, thereby cutting off power to the solid-state relays 20 andheating elements 15.

FIG. 3 is a block diagram illustrating one of the controllers 40. Eachcontroller 40 includes a microcontroller 48 and a user interface 50. Themicrocontroller 48 includes a processor 55 and memory 60. The processor55 receives inputs from the user interface 50 and temperature sensors25. The processor 55 then executes software stored in the memory 60. Theprocessor 55 (using the software) analyzes the received inputs andgenerates one or more control signals that control the solid-staterelays 20 and motor 11.

At least one controller 40 controls the speed of the motor 11, and thusthe speed of the conveyor 7. The controller 40 receives a user set cooktime input from the user interface 60 and controls the speed of themotor 11 based on the set cook time.

Each controller 40 further controls the temperature of the conveyor oven1. The temperature is based on a user set temperature entered into theuser interface 50. The controller 40 controls the temperature by turningthe solid-state relays 40 on or off which, in turn, controls power (onor off) being supplied to the heating elements 15. The controller 40controls the solid-state relays 40 depending on the current temperaturesensed by the temperature sensors 25 as compared to the user settemperature.

FIG. 4 is a process 70 for controlling the temperature of the conveyoroven 1, or more specifically, one set of the heating elements 15 (eitherupper or lower). The process 70 is performed when the controller 40receives a user set temperature from the user interface 50 (Step 71).The controller 40 then receives the temperature of the conveyor oven 1from the temperature sensors 25 (Step 72). The controller 45 thendetermines if the temperature of the conveyor oven 1 is above the userset temperature (Step 73). If the temperature of the conveyor oven 1 isabove the user set temperature, the controller 40 turns the solid-staterelays 20 off, thus cutting off power to the heating elements 15 (Step74). If the temperature of the conveyor oven 1 is not above the user settemperature, the controller 40 turns the solid-state relays 20 on, thusproviding power to the heating elements 15 (Step 75). The controller 40then cycles back to Step 71.

FIG. 5 is a circuit diagram illustrating the electrical components 10 ofa conveyor oven 1 with a bypass controller 100. The bypass controller100 is a controller used at startup of the conveyor oven 1 to create aburning arc across the contacts of the contactors 30A and 30B. The arcburns away oxidation on the contacts of the contactors 30A and 30B.Burning away contamination, such as oxidation, is sometime referred toas “wiping” the contacts or “cleaning” the contacts.

FIG. 6 is a block diagram illustrating the bypass controller 100 of theconveyor oven 1. The bypass controller 100 includes a microcontroller105. The controller 100 has an input 110 which is connected to a userpower switch 115. The controller 100 is also connected to solid-stateshorting relays 120, and provides commands and similar signal on anoutput 125 connected to the controller 40. In one embodiment, themicrocontroller is a Microchip model number PIC12F508 integratedcircuit. The microcontroller 105 generally includes a processor 130 anda memory 135. The processor 130 receives various inputs and executes asoftware program, stored in the memory 135, for analyzing the receivedinputs, and generates one or more control signals, or outputs. The userpower switch 115 is the main power switch of the conveyor oven 1 and islocated on the user interface 50. The bypass controller 100 receives asignal from the user power switch 115 (through input 110) when theconveyor oven 1 is turned on or off. The bypass controller 100 iselectrically coupled to the coils of the contactors 30A and 30B.

The solid-state shorting relays 120, when activated, short out thesolid-state relays 20. In other words, when the shorting relays 120 areturned on, a circuit path is created that bypasses the relays 20. Thus,the controller 100 can be considered or viewed as bypassing or shortingthe relays 20. As discussed in greater detail below, shorting the relaysis a first step in a process where contactors 30A and 30B are “wiped” orcleaned. Upon completion of the “wipe” process, the bypass controller100 sends a signal to the controller 40 through output 125 to continueoperation of the oven, as is further discussed below.

At startup or shutdown the bypass controller 100 receives a signal fromthe user power switch 115 at input 110. Upon receiving either signal,the bypass controller 100 activates the solid-state shorting relays 120.Activation of the shorting relays 120, shorts out the solid-state relays20. Once the solid-state relays 20 are shorted out, the contactors 30Aand 30B are connected directly in series with the heating elements 15.The bypass controller 100 then energizes the coils of the contactors 30Aand 30B. Once the coils are energized, the contacts of the contactors30A and 30B close. The heating elements 15 then draw a relatively largecurrent (approximately ten amps) through the contacts of the contactors30A and 30B. The ten amps of current create a burning arc across thecontacts. The arc “wipes” the contacts clean (or removes or reduces thecontamination, such as oxidation). The bypass controller 100 thende-activates the solid-state shorting relays 120, releasing the shortacross the solid-state relays 20. The bypass controller 100 then sends asignal to the controller 40 through the output 125. In the case ofstartup, the controller 40 receives the signal and begins normaloperation of the conveyor oven 1. In the case of shutdown, thecontroller 40 receives the signal and powers down the conveyor oven 1.In another embodiment the bypass controller 100 performs the “wiping”process upon user activation or other preprogrammed events. In such anembodiment, the conveyor oven 1 further includes a user bypass switch.Upon activation by a user, the user bypass switch sends a signal to thebypass controller 100. Upon receiving the signal, the bypass controller100 performs the “wiping” process.

FIG. 7 illustrates a process 200 for controlling the power to theheating elements 15 upon startup. The process 200 is performed when theconveyor oven 1 is powered on (Step 205). Once the conveyor oven 1 ispowered on and the bypass controller 100 receives the signal, the bypasscontroller 100 activates the solid-state shorting relays 120 to shortout the solid-state relays 20 (Step 210). The bypass controller 100 thenpowers the coils of the contactors 30A and 30B, thus closing thecontacts of the contactors 30A and 30B (Step 215). The heating elements15 draw approximately ten amps of current through the contacts of thecontactors 30A and 30B, creating a burning arc across the contacts (Step220). The bypass controller 100 then releases the short across thesolid-state relays 20 (Step 225). The bypass controller 100 then sends asignal to the controller 40 to begin normal operation of the conveyoroven 1, as discussed in process 70 (Step 230).

FIG. 8 illustrates a process 300 for controlling the power to theheating elements 15 upon shutdown. The process 300 is performed when theconveyor oven 1 is turned off (by the user or otherwise), and a signalis sent to the bypass controller 100 (Step 305). Before powering down,the bypass controller 100 activates the solid-state shorting relays 120to short out the solid-state relays 20 (Step 310). The heating elements15 draw approximately ten amps of current through the contacts of thecontactors 30A and 30B, creating a burning arc across the contacts (Step315). After a predetermined period of time, the bypass controller 100de-energizes the coils of the contactors 30A and 30B (Step 320). Thebypass controller 100 then de-activates the solid-state shorting relays120 (Step 325). The bypass controller 100 then sends a signal to thecontroller 40 to power down the conveyor oven 1 (Step 330).

Thus, the invention provides, among other things, a bypass circuit andwipe technique for contactors used to operate solid state relays thatcontrol heating elements of a conveyor oven. Various features andadvantages of the invention are set forth in the following claims.

What is claimed is:
 1. A control circuit for a cooking oven, the controlcircuit comprising: a contactor, the contactor including at least onecontact and at least one coil; a relay in series connection with thecontactor; a heating element controlled by the relay, the heatingelement in a series-type configuration with the relay and the contactor;and a controller configured to control a bypass of the relay, andactivate the at least one coil to provide power to the heating elementthrough the contactor.
 2. The control circuit of claim 1, wherein thebypass of the relay includes shorting the relay.
 3. The control circuitof claim 1, wherein the contactor and heating element are connecteddirectly in series when the relay is bypassed.
 4. The control circuit ofclaim 1, wherein the bypass of the relay and the power to the at leastone coil creates an arc across at least one contact.
 5. The controlcircuit of claim 1, wherein the controller is configured to control thebypass of the relay during startup of the cooking oven.
 6. The controlcircuit of claim 1, wherein the controller is configured to control thebypass of the relay during shut down of the cooking oven.
 7. The controlcircuit of claim 1, wherein the controller is configured to control thebypass of the relay upon activation of a user bypass switch.
 8. Acooking oven comprising: a housing; a heating element; and a controlcircuit, including a contactor, the contactor including at least onecontact and at least one coil; a relay in a series-type configurationwith the contactor and the heating element, the heating elementcontrolled by the relay; and a controller configured to control a bypassof the relay, and activate the at least one coil to provide power to theheating element through the contactor.
 9. The cooking oven of claim 8,wherein controlling a bypass of the relay includes shorting the relay.10. The cooking oven of claim 8, wherein the contactor and heatingelement are connected directly in series when the relay is bypassed. 11.The cooking oven of claim 8, wherein controlling a bypass of the relayand power to the at least one coil creates an arc across the at leastone contact.
 12. The cooking oven of claim 8, wherein the controller isconfigured to control the bypass of the relay during the startup of thecooking oven.
 13. The cooking oven of claim 8, wherein the controller isconfigured to control the bypass of the relay during shut down of thecooking oven.
 14. The cooking oven of claim 8, further including a userbypass switch, wherein the controller is configured to control thebypass of the relay upon activation of the user bypass switch.
 15. Amethod for controlling a cooking oven, the cooking oven including ahousing and a heating element, the method comprising: placing in aseries-type configuration, a relay, a contactor including at least onecontact and at least one coil, and the heating element; controlling abypass of the relay; and activating the at least one coil to providepower to the heating element through the contactor; wherein the heatingelement is controlled by the relay.
 16. The method of claim 15, whereincontrolling the bypass of the relay comprises shorting the relay. 17.The method of claim 15, wherein the contactor and heating element areconnected directly in series when the relay is bypassed.
 18. The methodof claim 15, wherein controlling the bypass of the relay and controllingthe power to the at least one coil creates an arc across at least onecontact.
 19. The method of claim 15, further including controlling thebypass of the relay during startup of the cooking oven.
 20. The methodof claim 15, further including controlling the bypass of the relayduring shut down of the cooking oven.
 21. The method of claim 15,further including controlling bypass of the relay upon activation of auser bypass switch.
 22. A method of controlling a cooking oven having atleast one heating element and at least one contactor, the at least onecontactor having an associated coil, the method comprising: receiving,at a controller, a signal from a user power switch; generating, with thecontroller, a signal to activate one or more first relays; shorting oneor more second relays subsequent to activating the one or more firstrelays; connecting the at least one contactor directly in series withthe at least one heating element; energizing the coil of the at leastone contactor to provide power to the at least one heating elementthrough the contactor; and de-activating the one or more first relays.